The present invention relates to a method of restoring or rehabilitating a pipe conduit. More particularly the method relates to softlining sewer rehabilitation.
Various methods of softlining a pipe conduit which is buried underground are known. Generally speaking, such methods involve the use of a flexible lining hose which is subsequently converted into a rigid liner by use of curable resins. The flexible lining hose (hence the term softlining) generally has a diameter which is slightly smaller than the inner diameter of the pipe conduit to be repaired. The lining hose frequently includes layers of resin-absorbing material and an essentially impermeable coating as the outermost layer. The resin-absorbing layer is soaked with an appropriate resin prior to introduction of the liner into the pipe conduit. The lining hose is introduced into the pipe conduit in a collapsed state and subsequently is shaped using a variety of means to conform the liner to the shape of the pipe conduit.
One method of this kind is shown in U.S. Pat. No. 4,009,063. This method employs a flexible lining hose with impermeable inner and outer layers of plastic with felt sandwiched between the plastic layers. In this method, bonding of the lining hose with the interior surface of the pipe conduit cannot take place due to the barrier created by the impermeable outermost layer of the lining hose. As a result leaky locations in the pipe conduit such as cracks, fissures, and damaged pipe connections are not sealed. This results in ground water penetrating into and collecting in the annular space between the liner and the pipe conduit. Further, securing the lining in the pipe conduit cannot be achieved in this construction because no bonding of the liner with the pipe conduit is possible. As a result the longevity of the rehabilitation is limited due to the corrosive effects of water in the annular spaces and the movement of the lining within the pipe conduit. Although a new liner has been installed, the pipe is not rehabilitated in effect because water continues to infiltrate. Another problem is encountered with this construction when the lateral lines which have been blocked off by the newly installed liner get reconnected. Because the installed liner is not secured, it may move in the axial direction while the cuts are being made or thereafter, and the reconnection lines cannot be adequately sealed at the joint. Leaky connections result and again the longevity of the liner is impaired.
Another softlining method is shown in U.S. Pat. No. 4,064,211 in which a lining hose is everted into the existing pipe conduit. In this method the lining hose is introduced into the interior of the pipe by turning one end region over and by causing the turned over region to gradually advance through the interior of the pipe conduit. During eversion the liner is turned inside-out so that the resin-soaked layer which was originally the inner layer of the lining hose is gradually turned to become the outermost layer of the lining hose. As it is everted, the liner is expanded by fluid which is used to turn the liner inside-out. Upon expansion of the reversed liner, the resin-soaked layer contacts and bonds the liner to the pipe conduit. Relatively high forces are needed to accomplish eversion of the resin-impregnated lining hose. Performing this eversion method frequently results in the formation of folds or creases in the lining hose which cannot be prevented. The shapes of folds and creases are stabilized when the resin cures or hardens. Such folds or creases adversely affect the flow-through cross-sectional area of the pipe; promote the formation of deposits in the new line; and prevent uniform contact of the lining hose to the wall of the existing pipe. When such folds or creases are formed, they must usually be removed by a milling apparatus or such similar techniques which result in increased costs.
Another softlining rehabilitation method is described in U.S. Pat. No. 4,770,562. In that patent the lining hose is comprised of an inner resin-absorbing layer and an impermeable outer layer which is perforated after impregnation with resin. In this method the plurality of flow through openings formed in the outer layer of the lining hose allow the resin to migrate from the inner layer to the pipe conduit surface, thereby bonding the liner to the wall of the existing pipe.
In performing these methods of softlining rehabilitation, it is desirable to have the resin fully impregnate the resin-absorbing layer of the lining hose. The resin-absorbing layer of the lining hose serves as a carrier for the resin which ultimately rigidifies and rehabilitates the pipe conduit. Impregnation is accomplished typically by evacuating air from the interstitial spaces of a resin-absorbing material such as felt. Evacuation of the air allows resin to fill the voids in the material. Various methods of performing impregnation using vacuum are known to those skilled in the art.
In performing vacuum impregnation generally, a vacuum pump is attached to one end of the lining hose or attached at various points along the lining hose. Upon creating a partial vacuum inside the lining hose, the resin is injected and pulled by the vacuum into the interstitial spaces of the resin-absorbing layer and down the length of the lining hose. To evacuate air from the resin-absorbing layer in any case, an outer layer of the lining hose must be essentially impermeable to fluids. Traditionally lining hoses have been constructed with an outermost layer or coating of plastic such as polyurethane, polyethylene, polyvinylchloride and other similar inert plastic materials. These plastics provide an essentially impermeable barrier on the outside of the lining hose and readily allow the creation of a partial vacuum inside the lining hose.
Although an essentially impermeable outer layer is needed to perform vacuum impregnation, it is not desirable to have an outer impermeable barrier against the existing pipe as shown in U.S. Pat. No. 4,009,063. If the outer impermeable layer of the lining hose lies directly against the pipe to create a barrier between the resin and the pipe conduit, the purpose of rehabilitation is somewhat defeated. If the resin is placed against the wall of the existing pipe using the eversion process shown in U.S. Pat. No. 4,064,211 other problems are encountered. The lining hose is traumatized during eversion because of the very high stresses needed to evert the resin-impregnated liner. Additionally, the lining hose is stretched and sometimes damaged due to the stresses encountered during eversion. Stretching of the liner leads to the formation of folds and creases and their associated problems discussed above.
The present invention provides a method for softlining rehabilitation in which a liner can be impregnated using vacuum and subsequently bonds to the pipe conduit without the disadvantages of the eversion methods. The present invention also provides a novel lining hose for use in softlining sewer rehabilitation.